System and method for reallocating a traffic channel in soft handoff state

ABSTRACT

There is disclosed, for use in a CDMA wireless network, a channel resource allocator for reallocating a data traffic channel in a soft handoff state to handle incoming calls from new mobile stations. The channel resource allocator includes an overhead channel controller for reconfiguring a data traffic channel as an overhead channel upon failure of an overhead channel element in a base transceiver station (BTS). The channel resource allocator determines if all data traffic channels of the BTS are in use. If so, the channel resource allocator determines whether any of the existing calls being serviced by the data traffic channels are in a soft handoff state in which the call is connected simultaneously to, two or more base transceiver stations. If so, the channel resource allocator drops the connection to the BTS in which the overhead channel failure occurred, thereby freeing up the data traffic channel. The overhead channel controller may then reconfigure the dropped data traffic channel as an overhead channel, or the channel resource allocator may reallocate the dropped data traffic channel to handle a new incoming call from a mobile station.

This application is a continuation of prior U.S. patent application Ser.No. 10/667,647 filed on Sep. 22, 2003, now U.S. Pat. No. 6,954,444 whichis a continuation of application Ser. No. 09/188,994, filed on Nov. 9,1998, now U.S. Pat. No. 6,625,134.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to CDMA wireless networksand, more specifically, to a system for reallocating a traffic channelin a soft handoff state as an overhead control channel or as a trafficchannel for another mobile station.

BACKGROUND OF THE INVENTION

Reliable predictions indicate that there will be over 300 millioncellular telephone customers by the year 2000. Within the United States,cellular service is offered not only by dedicated cellular serviceproviders, but also by the regional Bell companies, such as U.S. West,Bell Atlantic and Southwestern Bell, and the national long distancecompanies, such as AT&T and Sprint. The enhanced competition has driventhe price of cellular service down to the point where it is affordableto a large segment of the population.

Wireless subscribers use a wide variety of wireless devices, includingcellular phones, personal communication services (PCS) devices, andwireless modem-equipped personal computer (PCs), among others. The largenumber of subscribers and the many applications for wirelesscommunications have created a heavy subscriber demand for RF bandwidth.To maximize usage of the available bandwidth, a number of multipleaccess technologies have been implemented to allow more than onesubscriber to communicate simultaneously with each base transceiverstation (BTS) in a wireless system. These multiple access technologiesinclude time division multiple access (TDMA), frequency divisionmultiple access (FDMA), and code division multiple access (CDMA). Thesetechnologies assign each system subscriber to a specific traffic channelthat transmits and receives subscriber voice/data signals via a selectedtime slot, a selected frequency, a selected unique code, or acombination thereof.

Although TDMA-based wireless networks were developed on a large scalefirst, CDMA-based wireless networks are now also widely used. CDMAsystems divide the RF spectrum into a number of wideband digital radiosignals. Each digital radio signal carries several different coded“channels”. Each coded channel is distinguished by a uniquepseudo-random noise (PN) code used by the mobile station and/or the basestation. In a CDMA receiver, the coded channels are decoded by a signalcorrelator that matches PN sequences.

Some coded channels are used as data traffic channels to transportsubscriber voice and/or data signals, while other coded channels areused as control, or “overhead,” channels, including Pilot,Synchronization, Paging and Access channels. In some systems, one ormore of the Pilot, Synchronization, Paging and Access channels may becombined into a single channel.

When a mobile station accesses a base station in a CDMA wireless networkvia the overhead channels (each of which has a unique PN code), thenetwork assigns the mobile station to a data traffic channel (which hasa different PN code than the overhead channels) on which the mobilestation exchanges voice or data traffic with another party (includinganother mobile station), a data terminal, a fax machine, or the like.Typically, the coded overhead channels and the coded data trafficchannels used by the mobile station and the base station are on the sameRF carrier frequency. Advantageously, in many CDMA networks, theoverhead channels and the data traffic channels are on the same RFcarrier frequency in all cells (i.e., base station coverage areas) inthe networks.

Each data traffic channel and overhead control channel of a basetransceiver station constitutes a “resource” of that base transceiverstation. Ultimately, the channel resources of a base transceiver stationare limited by the practical restraints imposed by the hardware in thebase transceiver station. Thus, a base transceiver station is limited toservicing a certain number of data traffic channels at any one time.This limit is usually determined by the number of channeltransmitter/receiver elements that are built into the BTS. If a BTScontains fifty (50) channel transceiver elements that are reserved fordata traffic channels, then the BTS is limited to handling a maximum of50 two-way communication links with 50 mobile stations. If a fifty-firstmobile station tries to access the base transceiver station via itsaccess channel, the base transceiver station will refuse the accessrequest until one of the fifty data traffic channels becomes free.

The limitations on the number of data traffic channels served by a basetransceiver station also affect the failure recovery capabilities of abase transceiver station. If a hardware or software failure occurs in abase transceiver station, an overhead channel can be lost (i.e.,transmission failure) within the corresponding cell site. If the failureoccurs on the Paging, Synchronization, or Access channels, the existingcalls within the cell site are not lost. However, the failed basetransceiver station (BTS) becomes inaccessible and no new calls can beestablished. If the Pilot channel is lost, not only will the BTS becomeinaccessible, but all existing calls are dropped within a period of onlya few seconds.

To deal with the failure of an overhead channel, conventional wirelesssystems initiate an overhead channel switchover operation. When aswitchover occurs, the BTS reconfigures an unused data traffic channelto operate as an overhead channel by using the same PN code andfrequency range used by the failed overhead channel. This is an adequatesolution provided that the BTS is not operating at full capacity, suchthat all data traffic channels are already in use. If no data trafficchannel is available, the BTS drops an established call in order to freeup a data traffic channel that can be reconfigured as an overheadchannel. This is done even if the dropped call is a “911” emergency callor an important business or personal call. In any event, the droppedcall is a loss for the consumer and the service provider.

To overcome the problems associated with dropping an established call inorder to reconfigure an overhead channel, conventional wireless systemssometimes reserve a “hot” standby channel element for each overheadchannel. Unfortunately, this results in a loss of, for example, two tofour data traffic channels, depending on how many overhead channels areused to carry the Pilot, Synchronization, Paging and Access signals.

For example, if the Pilot, Synchronization, Paging and Access signalsare carried in four separate channels, four standby channels are neededand four data traffic channels are lost. If the Pilot and Paging signalsare carried in separate overhead channels and the Synchronization andAccess channels are combined in the same overhead channel, then threestandby overhead channels are needed and three data traffic channels arelost.

There is therefore a need in the art for a CDMA wireless network thatmore efficiently utilizes the channel resources of the base transceiverstations in the network in order to serve the greatest number of mobilestations possible. There is also a need for a CDMA wireless network thatsuffers minimal performance degradation upon the occurrence of a failurein an overhead channel. In particular, there is a need for a CDMAwireless network that minimizes the risk of dropping an existing call inorder to reconfigure a data traffic channel as an overhead channel. Moreparticularly, there is a need for a CDMA wireless network that minimizesthe risk of dropping an existing call in order to reconfigure a datatraffic channel and which eliminates or reduces the need for standbychannels.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object of the present invention to provide, for use in a CDMAwireless network, a channel resource allocator for reallocating a datatraffic channel in a soft handoff state to handle incoming calls fromnew mobile stations. The present invention further includes an overheadchannel controller for reconfiguring an overhead channel upon anoverhead channel failure in a base transceiver station (BTS). Thechannel resource allocator determines whether or not all data trafficchannels of the BTS are in use. If all data traffic channels are in use,the channel resource allocator determines whether any of the existingcalls being serviced by the data traffic channels are in a soft handoffstate in which the call is connected simultaneously to two or more basetransceiver stations. If so, the channel resource allocator drops theconnection to the BTS in which the overhead channel failure occurred,thereby freeing up the data traffic channel. The overhead channelcontroller may then reconfigure the dropped data traffic channel as anoverhead channel, or the channel resource allocator may reallocate thedropped data traffic channel to handle a new incoming call from a mobilestation.

If more than one existing call is in a soft handoff state, the channelresource allocator drops the connection that receives the weakestreverse channel signal from the mobile station. Additionally, thechannel resource allocator distinguishes between a “soft” handoffconnection between a first BTS and a second BTS and “softer” handoffconnection between separate sector antennas in the same BTS. The channelresource allocator drops soft handoff connections but not softer handoffconnections. Furthermore, in one embodiment of the present invention,the channel resource allocator may also distinguish between an“emergency” call and a “non-emergency call” in determining which one(s)of two or more soft handoff calls to drop in order to reconfigure anoverhead channel.

Accordingly, there is provided, in one embodiment of the presentinvention, for use in a wireless network comprising a plurality of basetransceiver stations, each of the base transceiver stations capable ofestablishing and maintaining communication links with a plurality of amobile stations by means of at least one overhead channel and aplurality of data traffic channels, an apparatus for allocating theplurality of data traffic channels comprising 1) at least one of: a) afailure detection circuit capable of detecting a failure in the at leastone overhead channel of a first base transceiver station and generatinga failure notification; and an access request detection circuit capableof detecting an access request message received from an accessing one ofthe plurality of mobile stations and generating an access requestnotification; and 2) a channel allocator capable of receiving at leastone of the failure notification and the access request notification and,in response thereto, terminating a first communication link between thefirst base transceiver station and a first selected one of the pluralityof mobile stations, wherein the first selected mobile station maintainsat least a second communication link with at least a second basetransceiver station, and at least one of: a) reconfiguring a first datatraffic channel associated with the terminated first communication linkas a replacement overhead control channel replacing the failed overheadcontrol channel and b) allocating the first data traffic channelassociated with the terminated first communication link to establish acommunication link with the accessing mobile station.

According to another embodiment of the present invention, the channelallocator is capable of determining if one of the plurality of datatraffic channels associated with the first base transceiver station isunused prior to terminating the first communication link between thefirst base transceiver station and the first selected mobile station.

According to still another embodiment of the present invention, thechannel allocator reconfigures an unused one of the plurality of datatraffic channels associated with the first base transceiver station asthe replacement overhead control channel in lieu of terminating thefirst communication link and reconfiguring the first data trafficchannel associated with the terminated first communication link.

According to still another embodiment of the present invention, thechannel allocator allocates an unused one of said plurality of datatraffic channels associated with said first base transceiver station toestablish a communication link with said accessing mobile station inlieu of terminating said first communication link and allocating saidfirst data traffic channel associated with said terminated firstcommunication link to establish a communication link with said accessingmobile station

According to yet another embodiment of the present invention, thechannel allocator further comprises a memory coupled to the overheadchannel controller, wherein the memory is capable of storing status dataassociated with the first communication link.

According to a further embodiment of the present invention, the statusdata comprises a received signal strength indicator associated with thefirst communication link.

According to a still further embodiment of the present invention, thestatus data comprises handoff state data, wherein the handoff state dataindicates whether the first selected mobile station associated with thefirst communication link maintains the at least a second communicationlink with the at least a second base transceiver station.

According to a yet further embodiment of the present invention, thehandoff state data indicates a total number of communication links thefirst selected mobile station maintains with other ones of the pluralityof base transceiver stations.

In yet another embodiment of the present invention, the status datafurther comprises a first received signal strength indicator associatedwith the first communication link and the overhead channel controllerterminates the first communication link with the first selected mobilestation if the first received signal strength indicator indicates that asignal associated with the first communication link is weaker that asecond signal associated with a second communication link between thefirst base transceiver station and a second selected one of theplurality of mobile stations.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention so that those skilled in the art maybetter understand the detailed description of the invention thatfollows. Additional features and advantages of the invention will bedescribed hereinafter that form the subject of the claims of theinvention. Those skilled in the art should appreciate that they mayreadily use the conception and the specific embodiment disclosed as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. Those skilled in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the invention in its broadest form.

Before undertaking the DETAILED DESCRIPTION, it may be advantageous toset forth definitions of certain words and phrases used throughout thispatent document: the terms “include” and “comprise,” as well asderivatives thereof, mean inclusion without limitation; the term “or,”is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, wherein likenumbers designate like objects, and in which:

FIG. 1 illustrates an exemplary CDMA wireless network according to oneembodiment of the present invention;

FIG. 2 illustrates a channel resource allocator in base stationaccording to one embodiment of the present invention;

FIG. 3 illustrates a flow diagram illustrating the operation of anoverhead channel controller in a base station according to oneembodiment of the present invention; and

FIG. 4 illustrates an exemplary message flow diagram in a wirelessnetwork according to one embodiment of the present invention.

DETAILED DESCRIPTION

FIGS. 1 through 4, discussed below, and the various embodiments used todescribe the principles of the present invention in this patent documentare by way of illustration only and should not be construed in any wayto limit the scope of the invention. Those skilled in the art willunderstand that the principles of the present invention may beimplemented in any suitably arranged CDMA wireless network.

FIG. 1 illustrates an exemplary CDMA wireless network 100 according toone embodiment of the present invention. The wireless telephone network100 comprises a plurality of cell sites 121-123, each containing one ofthe base stations, BS 101, BS 102, or BS 103. Base stations 101-103 areoperable to communicate with a plurality of mobile stations (MS)111-114. Mobile stations 111-114 may be any suitable cellular devices,including conventional cellular telephones, PCS handset devices,portable computers, metering devices, and the like.

Dotted lines show the approximate boundaries of the cells sites 121-123in which base stations 101-103 are located. The cell sites are shownapproximately circular for the purposes of illustration and explanationonly. It should be clearly understood that the cell sites may have otherirregular shapes, depending on the cell configuration selected andnatural and man-made obstructions.

In one embodiment of the present invention, BS 101, BS 102, and BS 103may comprise a base station controller (BSC) and a base transceiverstation (BTS). Base station controllers and base transceiver stationsare well known to those skilled in the art. A base station controller isa device that manages wireless communications resources, including thebase transceiver station, for specified cells within a wirelesscommunications network. A base transceiver station comprises the RFtransceivers, antennas, and other electrical equipment located in eachcell site. This equipment may include air conditioning units, heatingunits, electrical supplies, telephone line interfaces, and RFtransmitters and RF receivers. For the purpose of simplicity and clarityin explaining the operation of the present invention, the basetransceiver station in each of cells 121, 122, and 123 and the basestation controller associated with each base transceiver station arecollectively represented by BS 101, BS 102 and BS 103, respectively.

BS 101, BS 102 and BS 103 transfer voice and data signals between eachother and the public telephone system (not shown) via communicationsline 131 and mobile switching center (MSC) 140. Communications line 131may be any suitable connection means, including a T1 line, a T3 line, afiber optic link, a network backbone connection, and the like. Mobileswitching center 140 is well known to those skilled in the art. Mobileswitching center 140 is a switching device that provides services andcoordination between the subscribers in a wireless network and externalnetworks, such as the public telephone system. In some embodiments ofthe present invention, communications line 131 may be several differentdata links, where each data link couples one of BS 101, BS 102, or BS103 to MSC 140.

In the exemplary wireless network 100, MS 111 is located in cell site121 and is in communication with BS 101, MS 113 is located in cell site122 and is in communication with BS 102, and MS 114 is located in cellsite 123 and is in communication with BS 103. The MS 112 is also locatedin cell site 121, close to the edge of cell site 123. The directionarrow proximate MS 112 indicates the movement of MS 112 towards cellsite 123. At some point, as MS 112 moves into cell site 123 and out ofcell site 121, a “handoff” will occur.

A handoff transfers control of a call from a first cell to a secondcell. For example, if MS 112 is in communication with BS 101 and sensesthat the signal from BS 101 is becoming weak, MS 112 may then switch toa base station that has a stronger signal, such as the signaltransmitted by BS 103. MS 112 and BS 103 may then establish a newcommunication link and a signal is sent to BS 101 and the publictelephone network to transfer the on going voice, data, or controlsignals through BS 103. The call is thereby seamlessly transferred fromBS 101 to BS 103. An “idle” handoff is a handoff between cells of amobile device that is communicating in an overhead channel, rather thantransmitting voice and/or data signals in the regular traffic channels.

Because adjoining base stations in a CDMA network are operating on thesame RF carrier frequency, each of MS 111-114 station can simultaneouslyaccess two or more of BS 101-103 by using the same PN codes tocommunicate in data traffic channels and overhead channels with eachbase station. This enables a “soft” handoff to occur because a mobilestation can establish a second communication link (or “leg”) with asecond base station while still communicating on a first leg with afirst base station.

Advantageously, neither a mobile unit nor a wireless network mustimmediately sever a first communication link once a subsequentcommunication link has been established during a handoff operation.Thus, if the mobile station is within range of two or more basestations, it is possible for the mobile station to maintain multiple“legs,” each with a different base station, for a prolonged period oftime.

The present invention takes advantage of the fact that, if a BTS has notraffic channels available when a new mobile station tries to access theBTS or when a failure occurs in an overhead channel, there still isprobably at least one traffic channel in the BTS that is servicing anexisting call that is in a soft handoff state. The BTS can safely dropthe call connection in the traffic channel that is being used as one ofseveral soft handoff legs by the existing mobile station, because theexisting mobile station is still be connected to at least one BTS byanother soft handoff leg.

The present invention comprises a channel resource allocator forreallocating (or reassigning) a data traffic channel that is in softhand state. The present invention further comprises an overhead channelcontroller for reconfiguring a data traffic channel as an overheadchannel upon an overhead channel failure in a base transceiver station(BTS). If a new mobile station tries to access the BTS, or if anoverhead channel fails, the channel resource allocator determineswhether or not all of the data traffic channels of the BTS are in use.If all data traffic channels are in use, the channel resource allocatordetermines whether any of the existing calls being serviced by the datatraffic channels are in a soft handoff state to two or more basetransceiver stations. If so, the channel resource allocator drops one ofthese soft handoff connections to the BTS, thereby freeing up thecorresponding data traffic channel. If an overhead channel failureoccurred, the overhead channel controller reconfigures the newly freeddata traffic channel to replace the failed overhead channel. If a newmobile station is attempting to access the base transceiver station, thechannel resource allocator assigns the newly freed data traffic channelto the new mobile station.

FIG. 2 illustrates channel resource allocator 230 and overhead channelcontroller 230 in base station 101 according to one embodiment of thepresent invention. Base station 101 comprises base station controller(BSC) 210 and base transceiver station (BTS) 220. Base stationcontrollers and base transceiver stations were described previously inconnection with FIG. 1. BSC 210 manages the resources in cell site 121,including BTS 220. BTS 120 comprises BTS controller 225, which containschannel resource allocator 230 and overhead channel controller 231 inaccordance with the principles of the present invention. BTS 120 alsocomprises a channel controller 235, which contains representativechannel element 240, transceiver interface (IF) 245, RF transceiver unit250, antenna array 255, and channel monitor 260.

BTS controller 225 comprises processing circuitry and memory capable ofexecuting an operating program that controls the overall operation ofBTS 220 and communicates with BSC 210. Under normal conditions, BTScontroller 225 directs the operation of channel controller 235, whichcontains a number of channel elements, including channel element 240,that perform bi-directional communications in the forward channel andthe reverse channel. A “forward” channel refers to outbound signals fromthe base station to the mobile station and a “reverse” channel refers toinbound signals from the mobile station to the base station. The channelelements operate according to a code division multiple access (CDMA)protocol with the mobile stations in cell 121. Transceiver IF 245transfers the bi-directional channel signals between channel controller240 and RF transceiver unit 250.

Antenna array 255 transmits forward channel signals received from RFtransceiver unit 250 to mobile stations in the coverage area of BS 101.Antenna array 255 also sends to transceiver 250 reverse channel signalsreceived from mobile stations in the coverage area of BS 101. In apreferred embodiment of the present invention, antenna array 255 ismulti-sector antenna, such as a three sector antenna in which eachantenna sector is responsible for transmitting and receiving in a 120°arc of coverage area. Additionally, transceiver 250 may contain anantenna selection unit to select among different antennas in antennaarray 255 during both transmit and receive operations.

BSC 210 comprises BSC controller 211 and memory 212, which containschannel selection table 213. Channel selection table 213 storesinformation related to each of the “N” overhead and traffic channels inBTS 220 in a plurality of data fields, including a channel identifierfield (i.e., CID1 through CIDn), a channel type field (i.e., CTYPE1through CTYPEn), and a received signal strength indicator field (i.e.,RSSI1 through RSSIn), among others. Each of CID1-CIDn comprises a uniqueidentifier that identifies each channel element in channel controller235. Each of CTYPE1-CTYPEn comprises a plurality of sub-fields forstoring configuration and status information about a corresponding oneof CID1-CIDn. Each of RSSI1-RSSIn contains a value that indicates therelative strength of the signal being received in a correspondingchannel.

For example, the value in CID2 may identify an overhead channel that isbeing handled by channel element 240. CTYPE2 may contain a firstsub-field indicating that CID2 is a traffic channel, a second sub-fieldindicating that the traffic channel identified by CID2 is (or is not) asoft handoff leg to a mobile station that is in a soft handoff state,and a third sub-field indicating whether the soft handoff legcorresponds to a mobile station in a soft handoff state (i.e., handofffrom a first BTS to a second BTS) or in a softer handoff state (i.e.,handoff from a first antenna sector to a second antenna sector withinthe same BTS). CTYPE2 may contain a fourth sub-field indicating how manyother soft handoff legs are used by the mobile station, and which otherbase stations are handling the other soft handoff legs. Finally, RSSI2may contain a value indicating the relative strength of the signalreceived in the channel identified by CID2. RSSI2 may be measureddirectly by, for example, channel monitor 260, or may be determinedindirectly by monitoring the strength of the forward channel.

Much of the information stored in channel selection table 213 isreceived from BTS 220. However, some of the information stored inchannel selection table 213, such as information about other softhandoff legs, may be received from external sources, such as from otherbase transceiver stations controlled by BSC 210. The externally receivedinformation may also be received from other base station receivers viaMSC 140 and communications link 131.

FIG. 3 illustrates a flow diagram 400 illustrating the operation ofchannel resource allocator 230 and overhead channel controller 231 inbase station 101 according to one embodiment of the present invention.Under normal operations, forward and reverse channel signals areprocessed by the N channel elements under control of channel controller235. However, at some point in time, a new mobile station may attempt toaccess base station 101 when no additional traffic channels areavailable. Alternatively, an overhead channel may fail and the failureis subsequently detected in base station 101 by channel monitor 260(process step 301).

If a new mobile station attempts to access base station 101, channelcontroller 235 detects the corresponding access request message from thechannel element that is handling the access channel and notifies channelresource allocator 230 of the access request. Alternatively, if afailure occurred, channel monitor 260 notifies channel resourceallocator 230 and overhead channel controller 231 of the failure.Channel resource allocator 230 then determines if a data traffic channelis available (process step 302). Channel resource allocator 230determines whether a data traffic channel is available by requestingchannel status information from channel controller 235, which respondsby identifying inactive channel elements. Alternatively, channelresource allocator 230 may make this determination by requesting channelstatus information from BSC controller 211, which checks the contents ofchannel selection table 213 to determine if any data traffic channelsare not in use.

If one or more data traffic channels are available and a new mobilestation is attempting to access base station 101, channel resourceallocator 230 selects one of the available data traffic channels andsends a command to channel controller 235 that causes channel controller235 to assign one of its channel elements to the call from the newmobile station. If one or more traffic channels are available and anoverhead channel failure has occurred, channel resource allocator 230selects one of the available data traffic channels and sends a commandto overhead channel controller 231, which reconfigures one of theavailable channel elements in channel controller 235 as the failedoverhead channel (process step 303).

If no traffic channel is available, channel resource allocator 230retrieves from BSC controller 211 a list of traffic channels in BTS 220that are serving calls that are in soft handoff states and that havealready established two or more soft handoff legs (process step 304).BSC controller 211 determines this information from channel selectiontable 213.

If only one traffic channel forms a soft handoff leg for a mobilestation that is in a soft handoff state, then that soft handoff leg isdropped (process step 305). If more than one traffic channel forms asoft handoff leg for a mobile station that is in a soft handoff state,then channel resource allocator 230 examines the corresponding RSSI dataof each such soft handoff leg and determines which soft handoff leg hasthe weakest received signal in the reverse channel. The weakest softhandoff leg is then dropped (process step 306).

In one embodiment of the present invention, channel resource allocator230 determines which soft handoff leg is weakest by determining whichforward channel signal transmitted by BTS 220 to the soft handoff mobilestation is strongest. Generally, the stronger the forward channel signalused to communicate with a mobile station, the farther away the mobilestation is and the weaker its reverse channel signal is. Additionally,it is more likely that the most remote mobile station is receiving astrong forward channel signal in another soft handoff leg from anotherbase station, thereby minimizing the risk that the call will be droppedcompletely.

If a new mobile station is attempting to access base station 101,channel resource allocator 230 sends a command to channel controller 235that causes channel controller 235 to reassign/reallocate the channelelement that handled the dropped handoff leg to now handle the call fromthe new mobile station. Alternatively, if an overhead channel failureoccurred, channel resource allocator 230 sends a command to overheadchannel controller 231, which reconfigures the traffic channel elementfor the dropped handoff leg to replace the failed-overhead channel(process step 307). At this point, the mobile station that is in softhandoff is communicating with wireless network 100 via one or more othersoft handoff legs to other base transceiver stations.

FIG. 4 illustrates an exemplary message flow diagram 400 in wirelessnetwork 100 according to one embodiment of the present invention. Aftera failure in the overhead channel is detected or an access requestmessage is received when no data traffic channels are available, basetransceiver station 220 transmits a Request Message to base stationcontroller 210 requesting BSC 210 to identify those calls that are beinghandled by a traffic channel in BTS 220 that have the most soft handofflegs (message 401). BSC 210 responds with a Response Message thatreturns identification data identifying the call(s) with the most softhandoff legs (message 402).

Next, BTS 220 transmits a Handoff Direction Message to the mobilestation (labeled “handoff MS”) associated with the call identified byBSC 210 (message 403). The handoff mobile station then transmits aHandoff Completion Message to BTS 220 indicating that the handoff mobilestation is dropping the call (message 404). BTS 220 relays the HandoffCompletion Message to BSC 210 (message 405). Since the traffic channelpreviously used by the handoff mobile station is now available, BSC 210transmits a Traffic Channel Release Control Message to BTS 220 (message406). In response, BTS 220 transmits a Traffic Channel Release ControlAcknowledgment Message to BSC 210 (message 407).

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form.

1. For use in a wireless network capable of communicating with aplurality of mobile stations, a first base station comprising: a basetransceiver station, and a base station controller, wherein the basestation controller is configured to: detect a failure in an overheadchannel associated with the first base station; in response to thefailure in the overhead channel, identify a first mobile station with afirst communication link to the first base station and a secondcommunication link with a second base station, and terminate the firstcommunication link; and reconfigure resources associated with theterminated first communication link as a replacement overhead channelreplacing the failed overhead channel.
 2. The base station as set forthin claim 1 wherein the base station is further capable of determining ifone of a plurality of data traffic channels associated with the basestation is unused prior to terminating the first communication linkbetween the base station and the first mobile station.
 3. The basestation as set forth in claim 1 wherein the base station is capable ofdetermining a signal strength associated with each of a plurality ofcommunication links between the base station and a plurality of mobilestations, wherein each of the plurality of mobile stations maintains acommunication link with at least one other base station of the wirelessnetwork, and wherein the base station terminates a communication linkhaving the weakest signal strength and reconfigures the communicationlink having the weakest signal strength as the replacement overheadchannel.
 4. The base station as set forth in claim 1, wherein the basestation is further capable of determining that the first mobile stationhas established soft handoff legs with at least two base stations. 5.The base station as set forth in claim 2 wherein the base stationreconfigures an unused one of the plurality of data traffic channelsassociated with the base station as a second replacement overheadchannel and reconfigures the terminated first communication link as thesecond replacement overhead channel.
 6. For use in a wireless networkcapable of communicating with a plurality of mobile stations, a methodof allocating data traffic channels and overhead channels, the methodcomprising: detecting, by a base station controller, a failure in anoverhead channel of a base station; identifying a first mobile stationwith at a first communication link to a base station and a secondcommunication link to a second base station, terminating the firstcommunication link; and reconfiguring resources associated with theterminated first communication link as a replacement overhead channelreplacing the failed overhead channel.
 7. The method as set forth inclaim 6 further comprising determining if one of a plurality of datatraffic channels associated with the base station is unused prior to thestep of terminating the first communication link between the basestation and the first mobile station.
 8. The method as set forth inclaim 6 further comprising: determining a signal strength associatedwith each of a plurality of communication links between the base stationand a plurality of mobile stations, wherein each of the plurality ofmobile stations maintains a communication link with at least one otherbase station of the wireless network; and terminating a communicationlink having the weakest signal strength and reconfiguring thecommunication link having the weakest signal strength as the replacementoverhead channel.
 9. The method as set forth in claim 6, furthercomprising determining that the first mobile station has establishedsoft handoff legs with at least two base stations.
 10. The method as setforth in claim 7 further comprising reconfiguring an unused one of theplurality of data traffic channels associated with the base station as asecond replacement overhead channel and reconfiguring the terminatedfirst communication link as the second replacement overhead channel. 11.For use in a wireless network capable of communicating with a pluralityof mobile stations, a base station comprising: a base transceiverstation; and a base station controller, wherein the base stationcontroller is configured to: detect an access request message receivedfrom an accessing one of the plurality of mobile station, wherein theaccess request message is received during a period when no data channelsare available to the base station controller; select a first mobilestation from the plurality of mobile stations, wherein the selection ofthe mobile station is based upon the availability of communicationslinks to at least some of the plurality of mobile stations; terminate afirst communication link between the base station and the first mobilestation, wherein the first mobile station maintains at least a secondcommunication link with a second base station of the wireless networkupon the detection of the access request message; and reconfigure theterminated first communication link as a traffic channel forcommunicating with the accessing mobile station.
 12. The base station asset forth in claim 11 wherein the base station is further capable ofdetermining if one of a plurality of data traffic channels associatedwith the base station is unused prior to terminating the firstcommunication link between the base station and the first mobilestation.
 13. The base station as set forth in claim 11 wherein the basestation is capable of determining a signal strength associated with eachof a plurality of communication links between the base station and aplurality of mobile stations, wherein each of the plurality of mobilestations maintains a communication link with at least one other basestation of the wireless network, and wherein the base station terminatesa communication link having the weakest signal strength and reconfiguresthe communication link having the weakest signal strength as the trafficchannel for communicating with the accessing mobile station.
 14. Thebase station as set forth in claim 11, wherein the base station isfurther capable of determining that the first mobile station hasestablished soft handoff legs with at least two base stations.
 15. Thebase station as set forth in claim 12 wherein the base stationreconfigures an unused one of the plurality of data traffic channelsassociated with the base station as a second replacement overheadchannel and reconfigures the terminated first communication link as thesecond replacement overhead channel.
 16. For use in a wireless networkcapable of communicating with a plurality of mobile stations, a methodof allocating data traffic channels comprising: detecting an accessrequest message received from an accessing one of the plurality ofmobile stations; terminating a first communication link between a basestation and a first mobile station, wherein the first mobile stationmaintains at least a second communication link with a second basestation of the wireless network; and reconfiguring the terminated firstcommunication link as a traffic channel for communicating with theaccessing mobile station.
 17. The method as set forth in claim 16further comprising determining if one of a plurality of data trafficchannels associated with the base station is unused prior to terminatingthe first communication link between the base station and the firstmobile station.
 18. The method as set forth in claim 16 furthercomprising: determining a signal strength associated with each of aplurality of communication links between the base station and aplurality of mobile stations, wherein each of the plurality of mobilestations maintains a communication link with at least one other basestation of the wireless network; terminating a communication link havingthe weakest signal strength; and reconfiguring the resources associatedwith the terminated communication link having the weakest signalstrength as the traffic channel for communicating with the accessingmobile station.
 19. The method as set forth in claim 16, furthercomprising determining that the mobile station has established softhandoff legs with at least two base stations.
 20. The method as setforth in claim 17 further comprising reconfiguring an unused one of theplurality of data traffic channels associated with the base station as asecond replacement overhead channel and reconfiguring the terminatedfirst communication link as the second replacement overhead channel.